1. Field of the Invention
There has long been a need for flexible packaging materials which exhibit a high degree of transparency and provide an effective barrier to gas and moisture permeation. Additionally, there has been need, in such packaging materials, for resistance to high temperatures, and to boiling water in particular, to yield a so-called retortable package. This invention relates to transparent barrier films which can be used, among other things, as one component in flexible packaging materials to yield, among other things, retortable packages.
2. Description of the Prior Art
Coatings have been known which are inorganic in nature and which are made up of aluminum or ferric orthophosphate with some amount of tin; titanium, or zirconium. U.S. Pat. No. 3,853,591 discloses such coatings. Those coatings are transparent and exhibit good barrier qualities but not as good as are desired by users of such products. Moreover packaging materials made with such coatings fail within a few seconds of exposure to boiling water.
Films made from poly(vinyl alcohol), chemically-hardened or not, have been prepared for use in packaging materials but have been found to exhibit moisture sensitivity inconsistent with good, general, barrier properties.